BA.2.75.2: the new Omicron strain showing a worrying ability to evade immunity

Zhuang Pinghui in Beijing, South China Morning Post

Posted at Sep 28 2022 08:35 AM

Transmission electron micrograph of SARS-CoV-2 Omicron virus particles (orange) replicating within the cytoplasm of an infected CCL-81 cell (blue). Image captured at the NIAID Integrated Research Facility (IRF) in Fort Detrick, Maryland. Credit: NIAID
Transmission electron micrograph of SARS-CoV-2 Omicron virus particles (orange) replicating within the cytoplasm of an infected CCL-81 cell (blue). Image captured at the NIAID Integrated Research Facility (IRF) in Fort Detrick, Maryland. Credit: NIAID
  • The strain has two mutations that make it even more adept at locking on to human cells
  • Researchers in China say it has an unprecedented growth advantage

Scientists have identified a new strain of the Omicron coronavirus variant that, according to laboratory studies, is the most adept at dodging immunity.

The new strain, BA.2.75.2, is a sublineage of the BA.2.75 variant, which was initially reported in India in May and gained attention for its growth advantage.

The variant did not take off in a world dominated by BA.5.

But now the new BA.2.75.2 strain is looming as a bigger threat with two mutations that make it even more likely to bind to human cells for infection, according to researchers.

Worse still, the strain shows a strong ability to evade immunity from vaccination and previous infection, possibly making antibody treatments less effective.

A group of researchers from Imperial College London, the Karolinska Institutet and the University of Cape Town identified "extensive escape" by BA.2.75.2. On average, it is 6 1/2 times more difficult to neutralise, or block from infection, than BA.5, making it the most "neutralisation resistant variant" assessed to date, they said.

"These data raise concerns that BA.2.75.2 may effectively evade humoral immunity in the population," the researchers wrote in a paper on preprint site bioRxiv.org.

The World Health Organization is monitoring BA.2.75 and further subvariants as the virus continues to circulate at an "incredibly intense level" around the world.

Maria Van Kerkhove, the WHO's Covid-19 technical lead, said on Friday the agency was working with experts to assess the transmission and severity of the strain and the impact of countermeasures.

When asked about strains that could fuel an autumn wave, US infectious disease expert Anthony Fauci said last week that BA.2.75.2 appeared suspicious and might start evolving as another variant to cause such concern.

Separately, Chinese researchers from Peking University and the National Institutes for Food and Drug Control have found the new strain to have an "unprecedented" growth advantage.

In a paper also published on bioRxiv.org, the Chinese researchers said BA.2.75.2 exhibited the "most significant ability to escape immunity".

People previously infected with BA.5 had only a tenth of the ability to prevent reinfection with the new strain than they had against reinfection by BA.5, they said.

Compared to its parent BA.2.75, the new strain is 4.2 times more likely to cause breakthrough infections in people who have had three shots of Sinovac's vaccine.

It is also 5.9 times more likely to reinfect people who have been infected with BA.1, 6.2 times more likely to reinfect people who have been infected with BA.2 and 2.7 times more likely to reinfect people who have been infected with BA.5.

The BA.2.75.2 is particularly worrying because of its potential to make antibody infusions and other treatments less effective.

It is unclear how well existing vaccines, including the latest Omicron boosters, will be in fending off the new strain.

In correspondence published in the New England Journal of Medicine earlier this month, scientists reported the Moderna vaccine based on the original type of virus lost four times the ability to neutralise BA.2.75, but remained effective.

Peking University researcher Cao Yunlong, one of the lead authors of the Chinese study, expressed pessimism at the effectiveness of updated boosters, known as bivalent vaccines, against BA.2.75.2.

"I don't think the current wild type/BA.1 or wild type/BA.5 bivalent vaccines would be very effective against those convergent variants, based on the released mouse vaccination data," Cao wrote on Twitter.

Chinese researchers said the new strain showed a striking ability to evade existing antibody treatment.

The researchers called for close clinical monitoring of infections by this strain.

"The development of broad-spectrum Sars-CoV-2 vaccines and neutralising antibody drugs should be a high priority," they wrote.

Copyright (c) 2022. South China Morning Post Publishers Ltd. All rights reserved.